This invention relates to a control apparatus for an elevator in which a sinusoidal wave converter is used as a step up chopper during the stoppage of power supply, whereby a D.C. voltage twice as high as that in a prior art can be applied to an inverter so as to achieve a speed double that of the prior art with an accumulator of low voltage.
FIG. 4 is a circuit diagram showing the prior-art control apparatus for an elevator disclosed in the official gazette of Japanese Patent Application Laid-open No. 59-102770. Referring to this figure, letters R, S and T indicate the respective phases of a three-phase A.C. power source, which are connected through normally-open contacts 6a-6c and reactors 8a-8c to the input ends of a three-phase bridge rectifier circuit (hereinbelow, simply termed "rectifier circuit") which is constructed of diodes 1a-1f. The normally-open contacts 6a-6c are the normally-open contacts of a contactor (not shown) which is energized while the power source is normal.
A series circuit consisting of a normally-closed contact 7a and a battery BAT is connected across the input ends of the S-phase and T-phase of the rectifier circuit. The normally-closed contact 7a is the normally-closed contact of a contactor (not shown) which is deenergized while the power source stops.
Connected across the plus side and minus side output ends of the rectifier circuit are a smoothing capacitor 3, and a series circuit consisting of a resistor 4 and a transistor 5. This series circuit is for consuming regenerative power in the regenerative mode of operation.
In addition, the plus side output end and minus side output end of the rectifier circuit are connected to the input ends of an inverter in which power transistors 2a-2f and corresponding diodes are respectively connected in inverse parallel relationship. The output ends of the inverter are connected to a three-phase A.C. motor IM. The cage of the elevator, not shown, is driven by the three-phase A.C. motor IM.
Next, the operation of the prior-art apparatus will be described. While the elevator is run with the normal power supply, the normally-open contacts 6a-6c are closed, and the normally-closed contact 7a is open. Under this state, A.C. electric power from the three-phase A.C. power source R, S, T is fed to the rectifier circuit through the normally-open contacts 6a-6c as well as the reactors 8a-8c and is converted by the diodes 1a-1f into direct current, which is smoothed by the capacitor 3.
The D.C. electric power thus rectified and smoothed is applied to the inverter. This inverter applies alternating current of any desired voltage and any desired frequency (variable voltage and variable frequency) to the three-phase A.C. motor IM through the well-known pulse width modulation (PWM), whereupon the three-phase A.C. motor IM drives the cage (not shown) as specified by a speed command value.
On the other hand, when the power supply has stopped, the normally-open contacts 6a-6c are opened, and the normally-closed contact 7a is closed. Thus, the voltage of the battery BAT is applied across the A.C. input sides of the S-phase and T-phase of the rectifier circuit through the normally-closed contact 7a.
The voltage of the battery BAT is applied to the inverter, which drives the three-phase A.C. motor IM through the PWM control similarly to the foregoing.
During the stoppage of the power supply, however, the voltage of the battery BAT is lower than that of the normal power supply. When it is intended to forcibly raise the battery voltage, a large number of batteries must be connected in series, which is uneconomical. In general, therefore, the voltage of the battery BAT is set at several tenths of the voltage of the normal power supply, and the running speed of the cage is also lowered to several tenths in conformity with the set voltage, so that a high speed operation cannot be performed.
The rectifier circuit is constructed of the diodes 1a-1f, and is therefore simple in arrangement. Since, however, currents flowing through the A.C. power source contain higher harmonics of low orders of the fifth order, the seventh order, . . . etc. in considerable amounts, inductive disturbances are caused or the power factor is lowered by the higher harmonics. Therefore, the installed capacity of the power source enlarges disadvantageously.